They were an entirely different thing 70 years ago in Hollywood – eerie, decorous and called forth with incompetent cloudland simulations of voodoo. See Jacques Tourneur’s B-movie semi-classic “I Walked With a Zombie.”

Then came the original “Night of the Living Dead” by the cinematic auteur of Pittsburgh, George Romero. In one mini-budget film, he changed zombies forever. It just so happened that much of his financing came from a wholesale butcher. Hence, all manner of entrails, innards and offal could be made available to Romero to shoot with his zombies pretending it was their accustomed diet.

As everyone has known for a while now, zombies are big. “Night of the Living Dead” has spawned lots of zombie-lets, i.e. remakes and sequels as well as AMC’s “The Walking Dead,” and as many zombie fantasies from Robert Rodriguez as he can get away with.

It was only a matter of time before we saw Marc Forster’s “World War Z,” which would be the zombie movie to end all zombie movies if there were a snowball’s chance in hell that zombie movies would ever end (There isn’t. No money invested in a zombie movie is likely to be wasted.).

“World War Z” is the artful zombie blockbuster some have waited for. It stars Brad Pitt and is based on an extremely well-regarded novel written by Max Brooks, the zombie scholar son of Mel Brooks and Anne Bancroft (Please give that appositional phrase about 30 seconds to sink in fully.)

If we weren’t all flirting already with apocalypse fatigue – a mere day after the official beginning of summer – “World War Z” would have been far more impressive. But Hollywood’s big money minions have offered us so any variations on the end of us all, with cities being overrun and blown to Kingdom Come, that the rather genuine imaginative power and originality and even cinematic elegance of “World War Z” passes through making fewer ripples than it should.

Too bad. It’s a pretty good movie – absurdly overblown in the modern style of CGI-strewn A-movies with budgets in the hundreds of millions made out of B-movie ideas that used to be made on budgets of a buck and a quarter. It’s quite scary at times and suspenseful and often remarkably well-directed by Forster for what it is.

Brad Pitt plays a United Nations investigator and troubleshooter who discovers what’s going on in the worst possible way – in a monstrous traffic jam in Philadelphia where he’s trapped with his wife (Mireille Enos of TV’s “The Killing”) and his two daughters, one of whom is a severe asthmatic.

It takes a few minutes to discover that zombies are what’s causing the traffic jam, but it’s one of the several clever things about “World War Z” that it’s in no hurry to talk to you about zombies even though everyone seeing the movie knows what it’s about. Instead, you watch Pitt in the act of being a very devoted husband and warm, loving and protective father. One who, it just so happens, “used to work in dangerous places.”

After that, he is, of course, recruited out of semiretirement by the U.N. Deputy Secretary General to be the lead investigator of the U.N.’s zombie-fighting team.

So this fantasy moves from Philadelphia to South Korea to Jeruselam to Wales, while the dialogue has such flourishes as “Mother Nature is a serial killer … like all serial killers she can’t help secretly wanting to get caught.”

American soldiers’ name for the zombies is a generic “Zeke.” The Israelis – who are the first to figure out zombies were on the way in force – let in as many refugees as they can. “Everyone we save is one less zombie to fight,” they say.

At this point, the investigative plot gets the upper hand and it’s rather involving – as is the apocalyptic vision of zombie bodies swarming and piling up at giant Jeruselam walls like ants in an ant farm.

Anyone, in fact, with any experience of Gordon Douglas’ B-movie about giant ants, “Them,” is liable to spend a good deal of “World War Z” wondering why there is so much fruitless rifle shooting and so little flamethrowing. (We learned in “Them” that flamethrowers were the all-purpose large quantity destroyers of choice on the ground.)

We are, after all, told by “World War Z” these things: that loud noises attract zombies so you have to be quiet; the only bullets that stop them are successful “head shots”; and, when in doubt, burning “Zeke” will always get the job done.

Hence, my question is this: Why does no one at all ever break out the flamethrowers and napalm?

But that, no doubt, would have made for a much cruder, more practical and less upscale zombie spectacle than this one, which relates to zombie movies roughly the way the original “Alien” related to conventional horror movies.

“World War Z” was famously recut after original screenings. It’s quite suspenseful at the end, I assure you.

But what is unavoidable even at this early stage of the summer – with so many promising apocalyptic visions to come – is that it may be aimed at an audience suffering already more than a little from apocalypse fatigue.